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Parasite Ecology Ecology • The study of ecosystems – Interaction between organisms and the environment • Biotic – living part of environment • Abiotic – non-living part of environment Ecosystem • A grouping of plants, animals, and microbes occupying an explicit unit of space and interacting with each other and their environment. Ecological Niche • The role and organism plays in an ecosystem. – Dependant on location of host in the environment – Location within the host • Dimensions on a resource Distribution of Nematodes in the Eared Grebe Site of Infection • Coelozoic – Within a body cavity • Lumen of intestine, peritoneal cavity, bladder… • Histozoic – Within tissue • Muscle, blood, skin… Microenvironments • Differ in: – Nutrients – Oxygen – pH – Mobility – Immune cells Populations • All the individuals of a distinct species living within a specific ecosystem. – Infrapopulation • Within a single host – Metapopulation • Within a single host species – Suprapopulation • All stages all hosts Population Terminology • Intensity = # of parasites within a host. • Mean intensity = average number of parasites within infected hosts. • Prevalence = % infected. • Incidence = New Infection/time uninfected at start time • Density = total # in sampling unit. Macroparasites • Do not multiply in/on host. – Examples • adult cestodes and trematodes. – Aggregate populations • Crofton, 1970’s • Most parasites are within a few hosts. Aggregate Populations Microparasites • Multiply in/on host. – Examples • Plasmodium (malaria) • Trypanosomes (T. cruzi, Chagas disease) Population Structure • Which individuals are infected? • How is the infection distributed in the population? Susceptibility • Some individuals are more susceptible to infection. • Why? – Immune response? – Genetics? – Exposure? – Overall health and nutrition? Parasite Community • Multiple species of parasites within a host. • Often in different microenvironments within host. Reproduction • Finding a host = limiting factor. • Reproductive potential – Number of offspring • Reproductive success – Chance offspring find host • Low success = high potential • High success = low potential Increasing Reproductive Success • Viviparity – live birth. – Some nematodes. • Hermaphroditism – Insures fertilization and allows genetic diversity. • Asexual reproduction – Internal budding – Polyembryony – Schizogony Adaptations for Transmission • Altering appearance or behavior of host. Ants infected with nematode Epidemiology • Study of disease distribution – Vectors – transmit parasites – Nidus – set of environmental conditions that predict infection will occur. – Zoonoses – animal parasites that can infect humans. Co-evolution • Parasite and host co-evolve • Least virulent parasites can be very successful. • Parasite must evolve ways to counter immune response.